TINY OCEAN PLANTS NEED A BALANCED DIET

Upton, NY - Phytoplankton are the lungs - and the lifeline- of
the planet. But without a balanced diet that includes iron, these
tiny ocean plants cannot exhale the oxygen we humans breathe,
nor inhale the carbon dioxide we, our cars and our factories spew
out.

So report scientists from the U.S. Department of Energy's Brookhaven
National Laboratory and their colleagues, in two papers in Nature:
one in the October 10 issue, and one that appeared August 29.
Both describe results collected on two 1995 research cruises
- one near the Galapagos Islands, the other in the subarctic Pacific.
The studies' results add to what is known about an important
cornerstone of the global ecosystem.

On the Galapagos cruise, described in the Oct. 10 article, a
BNL-designed instrument helped prove that underachieving phytoplankton
could be revved up to consume more carbon dioxide if they got
an iron supplement.

The August article discussed a BNL-developed molecular detection
method that showed that subarctic phytoplankton are underproductive
because they're stressed for iron.

Both studies answer longstanding questions about phytoplankton.
But the scientists adamantly state that fertilizing the ocean
with iron would not be a "quick fix" for the potentially
climate-changing effects of humankind's carbon dioxide production.

"Too many factors would erase any increase in carbon dioxide
absorption, not to mention the risks of such a huge environmental
manipulation," said BNL oceanographer Michael Behrenfeld.

Phytoplankton are tiny single-celled plants, trillions of which
have floated freely on the ocean's surface for nearly 3.5 billion
years. Together, they process about 40 percent, or 43 billion
tons, of the world's carbon annually, much of it atmospheric carbon
dioxide.

When phytoplankton do not get all their necessary nutrients,
say the scientists, they cannot absorb as much carbon dioxide
as usual. The two cruises studied areas of ocean where phytoplankton
productivity is "limited" by lack of iron, so that they
cannot take full advantage of abundant nutrients such as nitrogen
and phosphorous.

Underwater Overachievers

In the Galapagos study, scientists fertilized an underproductive
patch of the South Pacific with iron three times over eight days,
while taking measurements to see how phytoplankton activity in
the 25-square-mile area changed.

The result was dramatic: Within 32 hours of the first application,
an area 6 miles wide and 81 feet deep turned green with phytoplankton.
The effect lasted two weeks.

Said Behrenfeld, "Our boat towed BNL's submersible instrument,
which repeatedly dove down to 200 feet and returned to the surface,
taking readings all the while. We could see immediately how the
phytoplankton responded to the iron - their photosynthetic efficiency
increased tremendously in the first 48 hours." A second
instrument inside the boat showed that the phytoplankton began
making much larger "antennae" to capture sunlight, in
order to take advantage of the iron-rich diet.

The team calls the effect "bottom up" control of phytoplankton,
to contrast it with the long-held "top-down" control
theory that says that tiny animals called zooplankton were eating
the phytoplankton as fast as they grew. The BNL scientists show
that it is nutrients, not grazing, that restricts the population.
But they stop far short of saying that adding iron to underproductive
patches of ocean could slow global climate change.

The experiment was led by scientists from Moss Landing Marine
Laboratories in California. The researchers who designed and
built Brookhaven's instruments with funding from the U.S. Department
of Energy and NASA also include BNL's Zbigniew Kolber and Paul
Falkowski, and scientists from Britain's Plymouth Marine Laboratory.

Lack of Iron Stresses Them Out

It may be easy to tell when humans are stressed, but what about
phytoplankton? BNL biochemist Julie LaRoche and her colleagues
reported in Nature on August 29 that they have devised
a phytoplankton stress test and used it in the waters off of Vancouver,
British Columbia.

The test takes advantage of the fact that phytoplankton living
in iron-poor oceans "make do" by substituting an iron-free
protein, flavodoxin, for their usual ferredoxin, which has to
be made with iron. "So, by detecting whether the phytoplankton
cell is making flavodoxin, we can tell if it's stressed for iron,"
LaRoche explained.

In May and September of 1995, LaRoche and her colleagues sampled
populations of diatoms, a kind of phytoplankton known to be particularly
sensitive to iron deficiency, at five stations in the ocean. Their
560-mile course ran from just off Vancouver to the center of the
Pacific Ocean.

After collecting the samples, they mixed phytoplankton cells
with antibodies that bound to flavodoxin and revealed how much
there was. They found that phytoplankton taken from off-shore,
iron-poor waters had nearly 200 times more flavodoxin than those
from fertile waters close to shore. The test may help oceanographers
with their experiments, since it can indicate phytoplankton iron-stress
levels in water samples carried home from a research cruise, without
sophisticated equipment or large-scale fertilization.

The study, which included scientists from the University of British
Columbia, the University of Delaware and the Plymouth Marine Laboratory,
was funded by DOE, the National Science Foundation and the Canadian
Joint Global Ocean Flux Study.

Brookhaven National Laboratory carries out basic and applied
research in the physical, biomedical and environmental sciences
and in selected energy technologies. Brookhaven is operated by
Associated Universities, Inc., a nonprofit research management
organizations, under contract with the U.S. Department of Energy.